The present invention relates to a transmission mechanism for a scanner, and more particularly to such a transmission mechanism which drives movable mechanisms of a scanner along a scanning path at a designed speed ratio.
In a regular scanner, as shown in FIG. 1, light from a light source is projected onto document and then reflected by document onto first reflector means, and then reflected by first reflector means to lens means through second and third reflector means, and then focused by leans means onto charge coupled device means. The light source and first reflector means form a scanning mechanism. The second and third reflector means for a reflecting mechanism moved along a scanning path in parallel to document. Further, a transmission mechanism is provided to move the scanning mechanism and the reflecting mechanism at a predetermined speed ratio. Various transmission mechanisms including screw transmission mechanism, gear transmission mechanism, belt transmission mechanism, etc., have been disclosed for this purpose. FIGS. 2A and 2B show a transmission mechanism for this purpose according to the prior art. This transmission mechanism comprises pulley type transmission unit and a belt type driving unit. The scanning mechanism is fixedly mounted on a fixed point at a rope of the pulley type transmission unit. The reflecting mechanism is pivoted to a movable pulley of the pulley type transmission unit. The pulley type transmission unit is driven by the belt type driving unit to move the scanning mechanism or the reflecting mechanism. The speed ratio between a fixed point at the rope of the pulley type transmission unit and the movable pulley is set at 2:1. When the belt type driving unit is started to move the scanning mechanism or reflecting mechanism, the scanning mechanism is moved, and the optical path between document and the charge coupled device is constantly maintained unchanged. However, because this design can only provide a speed ratio of 2:1, it application range is limited.